This invention relates to bifunctional additives for rubber compositions and their use in the stabilization of said compositions. More particularly, the invention relates to rubber compositions that possess a high degree of resistance to the detrimental effects of oxidative aging and metal corrosion over prolonged periods of time.
Essentially all types of rubber are known to be susceptible to deterioration resulting from prolonged exposure to atmospheric oxygen. The major cause of deterioration is the attack of oxygen on the olefinic unsaturation bonds contained in rubber. There is a general agreement that the presence of metals, particularly copper has an overall enchancing effect on the oxidizability of rubber. Although antioxidants have a beneficial effect on the rate of oxidative deterioration, the protective effect is relatively less if metal impurities are present in the rubber composition or the rubber is in contact with metals as, for example, in wire and cable applications.
Depending on the grade and type of rubber, antioxidants are generally selected with regard to the severity of processing and service of the finished article. For added protection, a copper inhibitor is incorporated into the composition.
Among the known antioxidants, arylamines are widely used to protect rubber against oxidative effects. However, arylamine-type antioxidants impart staining and discoloration of the vulcanized rubber. The demand for light colored heavy-duty rubber articles such as white wall tires, fixtures and wires has led to a search for nonstaining, nondiscoloring antioxidants with greater control over metal corrosion.
It has been now discovered that certain diarylamine derivatives of 1, 3, 4-thiadiazole prevent the detrimental effect of both oxygen and copper on the rubber composition. Furthermore, the bifunctional additives are nonstaining and may be used in black as well as light colored rubber articles.